Hello,
The following API returns a list of all users, including portal-only customers:
/rest/api/2/user/search/
I’m wondering if there is any way to filter out those service desk users? They appear in our dropdown and we would like to avoid it.
I will appreciate your guidance.
Edit: Ignore this response. As Fabien pointed out I did not see that this question was for Jira Server and this response is for Jira Cloud. 
Cloud-only: In the response to the rest/api/2/user/search there should be a parameter for each account called “accountType”. Portal-only accounts will have that value set to “customer”, while Atlassian accounts will be “atlassian”. So you should be able to filter by that value once you have the list.
I think you talk in about this doc ? /rest/api/2/users/search because the question concern jira server and the API that you talk concern Cloud 